The present invention relates to an arrangement for leak testing equipment consisting of a ventilator and of a breathing system provided between the ventilator and a patient, said ventilator comprising a gas delivery means and an expiration and inspiration valve, and said breathing system comprising at least tubing provided between the patient and the ventilator and a connector as well as possible other auxiliaries, the arrangement thus comprising a closing part, by means of which the connector can be closed during leak testing.
A ventilator can be defined briefly in the following manner. The purpose of a ventilator is to take care of the respiration of a patient and the change of gases when the patient's own spontaneous breathing is prevented. During anaesthesia, respiration is prevented due to administration of pharmaceuticals having a paralyzing effect on muscles and of anaesthetic gases. In intensive care, a patient may be connected to a ventilator to support spontaneous respiration.
The tubing by means of which breathing and anaesthetic gases are circulated between the lungs of a patient and an anaesthetic ventilator, and the bellows of the ventilator, valves, filters, directional valves, carbon dioxide absorber, a Y piece acting as a connector and possibly other auxuliaries associated with the tubing are referred to by a common term as a patient circuit or patient circulation.
As regards the patient circuit, it can be generally stated that the more connecting areas there are in the patient circuit, the greater is the likelihood of leaks.
Among the most common failures of equipments, taking place during anaesthesia and intensive care, are different leaks and detachments of tubes, the result of which may be, in the worst case, a prevention of the oxygen supply of the patient. Thus, a decrease in the oxygen content of blood, i.e. a hypoxia, is the most common cause of death related to anaesthetic accidents. The object of the automatic leak testing of the equipment is to prevent a hypoxia occurring during treatment, caused by internal leaks in the patient circuit, including the directional valves, absorbers and the Y piece, or in the ventilator.
However, it should be noted that a patient hazard can also be caused by an excess pressure in the patient circuit. Usually, a patient is connected to the patient circuit via an intubation tube and a Y piece, whereby the patient circulation and the lungs of the patient as well as the parts of the ventilator connected to the patient circulation have practically the same pressure. An increase in the pressure of the patient circuit is thus forwarded directly into the lungs, which expand as a result of the pressure. The expanding characteristics of lungs vary greatly between different patients; especially the lungs of child patients and those of patients whose lungs are seriously ill are inflexible, whereby the pressure rises rapidly dangerously high in the lungs of patients belonging to these patient groups. As a result of excess pressure, lung tissues may rupture or be otherwise damaged, whereby this may possibly result in intrapulmonary hemorrhages and even death in the worst case. Exactly corresponding damages may also be caused by excessive stretching of lungs due to excess pressure. In medicine, the exposure of lungs to excessive pressure is referred to by a term barotrauma.
To prevent leaks in a ventilator and the entire anaesthetic system, the equipment is checked thoroughly at least once a day, and a shorter check is carried out between operations, covering the patient circuit and other parts which are changed for hygiene reasons when a patient is replaced with another.
Leak testing is carried out daily manually when the equipment is started to be used by observing instructions drawn up by authorities or the hospital's own instructions, which are usually presented in the form of a checklist. The checklist may be a form attached to an anaesthetic record or a plastic-coated checklist hanging beside the apparatus, it being possible to erase entries made on said checklist before a new check begins.
In carrying out mechanical ventilation leak testing by means of a checklist, which may be for instance an FDA (Food and Drug Administration) format dating from 1992, an additional ventilation bag is first attached to the Y piece. The oxygen fresh gas flow is set to 250 ml/min, and the other fresh gas flows are closed. If an airway monitor adapter is connected to the circulation, it must be removed from the circulation before the test is started. Thereafter, the patient circuit is pressurized by using an emergency oxygen button, which causes a strong additional oxygen flow. The bellows of the ventilator rises to its upper position, and the breathing bag is filled with oxygen. The apparatus is allowed to ventilate for several respiratory cycles. At the same time, it is checked that the ventilator delivers the set batch volume to the bag during the inspiratory phase and that the bellows is filled in its entirety during the expiratory phase. If the bellows gradually starts to fill only partly, the patient circuit leaks.
Manual ventilation leak testing is carried out in the following manner. First, all fresh gas flows are closed. The APL valve is closed, and the connector, i.e. the Y piece, is stopped up with a finger. The patient circuit is pressurized to 30 cm H.sub.2 O by using an emergency oxygen button. The pressure must remain at this level for at least 10 seconds.
As an example of solutions known in the field, Cicero anaesthetic work stations manufactured by Dragerwerk AG can be mentioned, in which testing is performed in connection with starting the apparatus, but it can also be performed between patients. A Cicero workstation is provided with a closing part to which the Y piece is connected for the duration of the leak test. The purpose of the test is to detect leaks in the piston-cylinder unit and the tubes of the patient circulation. It does not detect leaks in the reservoir tube and the fresh gas section. With the use of Cicero workstation, it should be noted that the test must not be performed when the apparatus is connected to a patient.
One of the disadvantages of the test of the above-mentioned apparatus is that it includes no safety mechanism which would prevent leak testing when the patient tubing is connected to a patient. The pressure can be adjusted to no more than 40 mbar, and the duration of the test to 20-25 seconds. As regards a normal adult patient, this pressure is not yet life-threatening, but for a child patient and for a person with a lung condition it is hazardously high. Another disadvantage is that it must be indicated to a Cicero workstation when the Y piece is stopped up and when it is not stopped up.
Another example of prior art is a solution where the basic principle is the same as in the above-mentioned solution based on an FDA checklist, but the difference is that some phases are automatized. Before a leak test is started, some procedures must be performed manually, however. The fresh gas flows must be closed. The laughing gas can be restricted by means of a solenoid valve, so that it could also be shut off automatically. On the other hand, the oxygen and air must be shut off manually. The system measures fresh gas proportions and detects when the fresh gas flows are approximately closed. The AUTO/MAN valve of this solution is manually operated, wherefore the user has to turn the valve to the correct position if it is not in the position required by the leak test. The system recognizes the position of the AUTO/MAN valve automatically. When the valve is in the correct position, the system acknowledges the valve as turned.
The disadvantage of the solution presented above is that the Y piece must be stopped up manually and that the user of the system must indicate to the software that the Y piece is stopped up, because the system is not capable of observing automatically if the Y piece is stopped up in the correct manner, i.e. if the closing part is used in the correct manner or not.